Drug delivery systems which allow for efficient absorption of biological agents into the circulation and which increase effective bioavailability of the agent in the circulation for effective therapy are available, but they are not all devoid of potential risks or unwanted side effects. To overcome these challenges, drug delivery systems, such as microparticles and microspheres that are small enough for administration by inhalation in a safe and effective manner have been developed.
For example, microparticles of 2,5 diketopiperazines have been shown to be useful in drug delivery, particularly those bearing acidic R groups (see for example U.S. Pat. No. 5,352,461 entitled “Self Assembling Diketopiperazine Drug Delivery System;” U.S. Pat. No. 5,503,852 entitled “Method For Making Self-Assembling Diketopiperazine Drug Delivery System;” U.S. Pat. No. 6,071,497 entitled “Microparticles For Lung Delivery Comprising Diketopiperazine;” and U.S. Pat. Nos. 6,331,318; 6,395,774; 6,663,898; 6,906,030; and 7,276,534 each entitled “Carbon-Substituted Diketopiperazine Delivery System)” each of which is incorporated herein by reference in its entirety, for all that it teaches regarding diketopiperazines and diketopiperazine-mediated drug delivery). Diketopiperazines can be formed into particles that incorporate a drug or particles onto which a drug can be adsorbed. The combination of a drug with a diketopiperazine can impart improved drug stability and delivery of the active agent. These particles can be administered by various routes of administration. As dry powders these particles can be delivered by inhalation to specific areas of the respiratory system, depending on particle size.